<template>
  <ul class="list">
    <li class="item" v-for="item of letters" :key="item" :ref="item" @click="handleLetterClick" @touchstart="handleTouchStart" @touchmove="handleTouchMove" @touchend="handleTouchEnd">{{item}}</li>
  </ul>
</template>

<script>
export default {
  name: 'CityAlphabet',
  props: {
    list: Object
  },
  computed: {
    letters () {
      const letters = []
      for (let i in this.list) {
        letters.push(i)
      }
      return letters
    }
  },
  data () {
    return {
      touchstatus: false,
      startY: 0,
      timer: null
    }
  },
  updated () {
    this.startY = this.$refs['A'][0].offsetTop
  },
  methods: {
    handleLetterClick (e) {
      this.$emit('change', e.target.innerText)
    },
    handleTouchStart () {
      this.touchstatus = true
    },
    handleTouchMove (e) {
      if (this.touchstatus) {
        if (this.timer) {
          clearTimeout(this.timer)
        }
        this.timer = setTimeout(() => {
          const startY = this.startY
          const touchY = e.touches[0].clientY - 79
          const index = Math.floor((touchY - startY) / 22)
          if (index >= 0 && index <= this.letters.length) {
            this.$emit('change', this.letters[index])
          }
        }, 16)
      }
    },
    handleTouchEnd () {
      this.touchstatus = false
    }
  }

}
</script>

<style lang="stylus" scoped>
  .list
    position: absolute
    top: 1.8rem
    right: 0
    width: .64rem
    text-align: center
    display:flex
    flex-direction: column
    .item
      color:#25a4bb
      line-height: .44rem
</style>
